1. Field of the Invention
The present invention relates to a position detection system for a mobile object, more specifically, relates to a position detection system, which can measure a position (distance and direction) of the mobile object adapted to move around a predetermined area. Additionally, the present invention relates to a motion control of a robot adopting this system.
2. Description of Relevant Art
In recent years, an autonomous mobile robot has been developed. Especially, the recent developments in this technique have been focused on an autonomous bipedal walking robot.
Additionally, a voice recognition apparatus which converts a voice message to text data and a voice synthesis apparatus which sounds a synthesized voice by synthesizing the synthesized voice from text data have been developed, and have been adopted for various apparatus. A mobile robot equipped with such kind of apparatuses, i.e. a voice recognition apparatus and a voice synthesis apparatus, which are adapted in order to have a dialogical communication with a person, has been developed.
For realizing an autonomous communication between a mobile robot and a person, the mobile robot has to search and identify a person and has to move toward the identified person.
For achieving this requirement, an apparatus, which detects a presence of a target object within a specific area and measures the position within the specific area of the detected target objects, and the method thereof have been developed.
As an example of these conventional apparatus, apparatuses disclosed in Japanese unexamined patent publications, such as JP2002-307338, JP2003-91678, and JP2002-98749, have been discovered.
The apparatus disclosed in JP2002-307338 detects a presence of a target object by checking whether or not an infrared radiation from the target object is sensed by an infrared sensor (human sensor).
The apparatus disclosed in JP2003-91678 detects a presence of a target object using a plurality of detectors which are disposed within a specific area, and the position of the detector which sensed the target object is regarded as the position of the target object.
The apparatus disclosed in JP2002-98749 detects a presence of a target object using a plurality of transmitters, which are disposed within a specific area, and a transmitter, which is provided on a target object. In this apparatus, field intensity of radio wave transmitted from the target object's transmitter and field intensity of radio wave transmitted from the transmitter provided within the specific area are computed, and the position of the target object is measured using these computed field intensities.
In the case of JP2002-307338, however, the detection of the target object can be achieved only when the target object is within a detectable range of the infrared sensor (human sensor). That is, if the target object is out of the detectable range, the detection of the target object cannot be achieved.
In the case of JP2003-91678 and JP2002-98749, following defects exist. (1) Since a plurality of detectors or transmitters are required for detecting a target object, the cost of the apparatus becomes high; (2) If a target object moves around the wide range, the detection of the target object can be achieved only when the target object is within the specific area where detectors and transmitters are provided; and (3) Rough position of the target object can be measured but the accurate position of the target object, such as a direction and distance from the detector (transmitter), cannot be measured.
Here, if at least one of the target object and the detector is a mobile object, e.g. if the target object is a mobile object and the detector itself is a mobile robot, the area where the mobile robot is installed for detecting a person changes continuously. In this case, since the provision of a plurality of detectors and transmitters in the area beforehand is simply impossible, the apparatuses disclosed in above references were inadequate apparatuses.
In the case of conventional apparatuses, i.e. an apparatus for measuring the position of the mobile object, there have been the following defects. That is, since the manufacturing cost of RFID is low, the problem due to cost does not occur when RFID is used as transmitter, even if the number of the person to be detected is increased. But, since power of radio wave is small, the adaptable range of the apparatus is limited to a narrow range.
When increasing the adaptable range of the apparatus, however, the transmitter whose power of radio wave is much high or a plurality of receivers, which are provided at a predetermined interval, is required. In this case, the adoption of the transmitter having high power increases the manufacturing cost thereof, and causes the problems in cost if each person is provided with the transmitter having high power.
Additionally, if a plurality of receiver is provided at a predetermined interval, this requires the cost of infrastructure and limits the adaptable range to a narrow range. Additionally, since attenuation of radio wave transferred from the transmitter occurs if obstacle exists in a predetermined area, this decreases the accuracy in the position detection of the target object.
In the case of the apparatus disclosed in JP2002-98749, since attenuation of radio wave transferred from the transmitter occurs if RFID is used as the transmitter and obstacle exists in the specific area, this decreases the accuracy in the position detection of the target object.
Therefore, a system, which can detect with accuracy the position within a wide controlled area of the target object without requiring additional equipments even if the transmitter whose transmission power is small is adopted as the transmitter on the mobile object, has been requested.